Surface treatment method

ABSTRACT

According to the present invention, a plasma treatment process is performed for a surface of a metal film exposed through a resin layer, including a foreign resin substance attached to the surface, so that the foreign resin substance can be roughened without substantially damaging the resin layer; and the entire exposed surface of the metal film is etched, using a spray etching method for which an etching fluid is ejected through a nozzle, and the foreign resin substance is removed from the exposed surface.

BACKGROUND OF THE INVENTION

The present invention relates to a surface treatment method, and relates in particular to a surface treatment method for easily removing a foreign resin substance that has been attached to the exposed surface of a metal film.

During the processing performed to produce a printed circuit board to be used, for example, for semiconductor devices, a pad is prepared, as shown in FIG. 5, on one face of a printed circuit board 10, for the formation thereon of a solder bump 18 that will serve as an external connection terminal. Specifically, the structure of this pad includes a metal film 12, such as a copper film, deposited on the face of the printed circuit board 10, a resin layer 14, such as a solder resist layer, that covers the peripheral edges of the metal film 12, and a protective metal layer 16 that is formed on and covers the exposed surface of the metal film 12. By constructing the pad in this manner, the formation of an oxide film on any exposed surface is prevented.

Further, since generally, either electroplating or electroless plating is used to form the protective metal layer 16, for this operation to be successfully performed and the protective metal layer 16 uniformly deposited, it is vital that there be no oxide film formed on and no foreign substances adhering to the exposed surface of the metal film 12.

Therefore, a method has been proposed, in patent document 1, whereby soft etching is performed to clean the exposed surface of the metal film 12 and to remove an oxide film that may have been formed there.

However, after the resin layer 14 has been deposited, the possibility exists that, as shown in FIG. 6, a foreign resin substance 20 may become attached to the exposed surface of the metal film 12. And since in such a case the foreign resin substance 20 and the resin layer 14 are heated together, the foreign resin substance 20 may be firmly attached to the exposed surface.

In such a case, following the performance of soft etching for the exposed surface of the metal film 12, the portion of the exposed surface to which the foreign resin substance 20 is attached may be unaffected by the etching, as shown in FIG. 7, leaving the foreign resin substance 20 attached to the exposed surface. Should this occur, and should electroplating or electroless plating be used to form the protective metal layer 16, the plating process could not be successfully performed, since the protective metal layer 16 would neither be deposited on nor cover the surface portion to which the foreign resin substance 20 is attached.

To correct this shortcoming, a remedial method proposed in patent document 2 provides for the performance of a plasma treatment process to remove the foreign resin substance 20 from the exposed surface of the metal film 12.

-   [Patent Document 1] JP-A-2004-124110 -   [Patent Document 2] JP-A-2007-336321

It has been determined that a foreign resin substance 20 can be completely removed by employing the surface treatment method proposed in patent document 2, for performing a plasma treatment process to remove a foreign resin substance 20 from the exposed surface of the metal film 12.

It has also been determined, however, that when the plasma treatment process is employed to completely remove the foreign resin substance 20, the process performed in this case continues and extensively damages the resin layer 14.

SUMMARY OF THE INVENTION

Therefore, one objective of the present invention is to resolve this conventional problem, which is occasioned by the extensive damage sustained by a resin layer when the plasma treatment process is employed to completely remove, from a metal film surface exposed through the resin layer, an attached foreign resin substance, by providing a surface treatment method whereby, without substantially damaging a resin layer, a foreign resin substance and an oxide film can be removed from the surface of a metal film exposed through the resin layer.

[Means for Solving the Problems]

Through studies performed to resolve the problem, the present inventors found that, substantially, the resin layer does not suffer extensive damage when the foreign resin substance is merely roughened by the plasma treatment process.

Furthermore, the present inventors found that when a nozzle is used to spray etching fluid onto a metal film, etching of the surface of the metal film occurs along the circumferential edge of the foreign resin substance that is attached, and the foreign resin substance can be easily removed. Thus, the present inventors are encouraged to initiate the process to prepare the present invention.

That is, according to a first aspect of the invention, there is provided a surface treatment method including the steps of:

preparing a surface of a metal film exposed through a resin layer, including a foreign resin substance attached to the surface;

performing a plasma treatment process for the surface so as to roughen the foreign resin substance without substantially damaging the resin layer; and

etching the entire exposed surface of the metal film, with using a spray etching method for which an etching fluid is ejected through a nozzle to remove the foreign resin substance from the exposed surface.

According to a second aspect of the invention, there is provided the surface treatment method according to the first aspect, wherein

the metal film is deposited on at least one face of a printed circuit board, and

the surface of the metal film exposed through the resin layer is located on the same circuit board side as a pad on which an external connection terminal is formed.

According to a third aspect of the invention, there is provided the surface treatment method according to the first aspect, wherein

a copper film is deposited, as a metal film, and

soft etching is performed, with using a spray etching method, so as to remove an oxide film from an exposed surface of the copper film.

According to a forth aspect of the invention, there is provided the surface treatment method according to the first aspect, wherein

a metal plated film is deposited with using plating as the metal film.

According to a fifth aspect of the invention, there is provided the surface treatment method according to the first aspect, wherein

the pressure setting for the ejection, through the nozzle, of the etching fluid is from 0.1 to 0.3 MPa.

According to a sixth aspect of the invention, there is provided a surface treatment method including the steps of:

preparing a surface of a metal film exposed through a resin layer, including a scratch formed on the surface, and

etching the entire exposed surface of the metal film, with using a spray etching method for which an etching fluid is ejected through a nozzle to remove the scratch from the exposed surface.

According to a seventh aspect of the invention, there is provided the surface treatment method according to the sixth aspect, wherein

the metal film is deposited on at least one face of a printed circuit board, and

the surface of the metal film exposed through the resin layer is located on the same circuit board side as a pad on which an external connection terminal is formed.

According to an eighth aspect of the invention, there is provided the surface treatment method according to the sixth aspect, wherein

a copper film is deposited, as a metal film, and

soft etching is performed, with using a spray etching method, so as to remove an oxide film from an exposed surface of the copper film.

According to a ninth aspect of the invention, there is provided the surface treatment method according to the sixth aspect, wherein

a metal plated film is deposited with using plating as the metal film.

According to a tenth aspect of the invention, there is provided the surface treatment method according to the sixth aspect, wherein

the pressure setting for the ejection, through the nozzle, of the etching fluid is from 0.1 to 0.3 MPa.

According to this invention, the metal film is deposited on at least one face of a printed circuit board, and the metal film surface exposed through the resin layer is located on the same circuit board side as a pad on which an external connection terminal is formed. With this arrangement, the pad face used to mount the external connection terminal on the printed circuit board can be easily prepared.

In addition, a copper film is deposited, as a metal film, and soft etching is performed, using a spray etching method, to remove an oxide film from an exposed surface of the copper film. With this arrangement, a uniform, exposed surface can be obtained for the copper film from which an oxide film has been removed.

Further, a metal plated film, deposited using plating, is appropriate as a metal film.

According to this invention, first, a plasma treatment process is performed, to roughen a foreign resin substance that is attached to the surface of a metal film exposed through a resin layer. It is considered proven that roughening of a foreign resin substance can reduce the adhesiveness evidenced by a foreign resin substance that is attached to an exposed surface of a metal film.

Generally, since a foreign resin substance is much thinner than a resin layer and considerably smaller than an exposed surface of a metal film, when the foreign resin substance is roughened during the plasma treatment process, the resin layer is only superficially damaged, and on the whole, the state of the resin layer remains the same as before the plasma treatment is performed.

Then, the exposed surface of the metal film to which the roughened, foreign resin substance is attached is etched using a spray etching method, according to which an etching fluid is ejected through a nozzle. The etching fluid does not etch the foreign resin substance directly. However, because of the tendency of the etching fluid to gradually permeate the roughened foreign resin substance and the ejection pressure applied to the etching fluid, etching of the surface of the metal film occurs along the peripheral edge of the foreign resin substance. As a result, the foreign resin substance can be completely removed.

During this spray etching process, the exposed surface of the metal film is selectively etched, so that the exposed surface of the metal film can be smoothed and leveled to remove scratches, and oxide film on the exposed surface of the metal film can be removed.

As a result, the surface of the metal film exposed through the resin layer can be smoothed and oxide film formations can be removed, and electroplating or electroless plating can be employed to form a uniform protective metal layer on the exposed surface of the metal film.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram for explaining the state wherein a foreign resin substance, attached to the exposed surface of a metal film, can be removed by using spray etching.

FIGS. 2A to 2C are diagrams for explaining the process for smoothing, using spray etching, the exposed surface of a metal film that is scratched.

FIGS. 3A and 3B are microscope photographs, according to one example of the present invention, of pad faces exposed on a printed circuit board before a plasma treatment is performed, and of the pad faces on the printed circuit board after the plasma treatment and spray etching processes have been performed.

FIGS. 4A and 4B are microscope photographs, according to a comparison example, of pad faces exposed on a printed circuit board before a plasma treatment process is performed, and of the pad faces on the printed circuit board after the plasma treatment and spray etching processes have been performed.

FIG. 5 is a diagram for explaining the structure of a pad face on a printed circuit board.

FIG. 6 is a diagram for explaining the state wherein a foreign resin substance is attached to the surface of a metal film, exposed through a resin layer, that forms a pad face.

FIG. 7 is a diagram for explaining the state wherein a foreign resin substance, attached to the exposed surface of the metal film, is not removed, even after the exposed surface is immersed in an etching fluid.

FIG. 8 is a diagram for showing processes in an apparatus for performing a spray etching.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In one embodiment of the present invention, first, the plasma treatment process is performed to roughen a foreign substance formed by a resin, such as a solder resist, that has been attached to the surface of a metal film, such as a copper film, exposed through a resin layer, such as a solder resist layer.

It is preferable that a plasma used for the plasma treatment process employ either an O₂, He or Ar gas and have an output of about 100 to 400 W.

Further, during the plasma treatment process, it is preferable that the plasma irradiation of an object, such as the surface of a metal film, deposited on a printed circuit board, that is exposed through a resin layer, be performed under a reduced pressure for a period of from 100 to 500 seconds, or more preferably, of from 200 to 300 seconds. When a plasma irradiation period of less than 100 seconds is used, appropriate roughening of a foreign resin substance tends to be difficult. On the other hand, when a plasma irradiation period exceeding 300 seconds is used, although a foreign resin substance can be appropriately roughened, resin layer damage tends to be increased.

Following this, a spray etching method is employed during which an etching fluid is ejected and sprayed on the metal film, through a nozzle, to etch the exposed surface of the metal film to which a foreign resin substance, roughened by the plasma treatment, is attached. For this etching process, it is preferable that the pressure setting for the ejection, through the nozzle, of the etching fluid be from 0.1 to 0.3 MPa, so that the exposed surface of the metal film can be etched to a depth of 1 to 3 μm.

During the spray etching process, the etching fluid does not etch the resin layer and the foreign resin substance; however, as shown in FIG. 1, the surface of a metal film 12, onto which the etching fluid is ejected, is etched. That is, the surface of the metal film 12 is etched along the peripheral edge of an attached foreign resin substance 20, and as a result, the adhesiveness exhibited by the foreign resin substance is considerably reduced.

Furthermore, since the surface of the metal film 12, to which the foreign resin substance 20 is attached, is etched as the etching fluid permeates the roughened foreign resin substance 20, the adhesiveness exhibited by the foreign resin substance 20 is further reduced.

Since the adhesiveness exhibited by the foreign resin substance 20 is considerably reduced, the foreign resin substance 20 can be easily removed from the surface of the metal film 12 using the pressure employed to eject the etching fluid through the nozzle.

After the foreign resin substance 20 has been removed, additional etching of the exposed surface of the metal film 12 may be performed, as needed, using dip etching, for which the exposed surface is immersed in an etching fluid.

Besides, the spray etching processes are performed by, for example, the apparatus as shown in FIG. 8.

However, in a case wherein instead of the spray etching process dip etching is performed, i.e., in this case, wherein the exposed surface of the metal film 12, to which the foreign resin substance 20, roughened by plasma treatment, is attached is immersed in an etching fluid, the foreign resin substance can not be removed. This is probably because only a small amount of the etching fluid has permeated the roughened foreign resin substance, and although the adhesiveness of the foreign resin substance 20 is reduced, the surface of the metal film 12 to which the foreign resin substance 20 is attached can not be appropriately etched.

Furthermore, when the spray etching method is employed, selective etching of the exposed surface of a metal film 12 is enabled, and even the exposed surface of a metal film 12 that has been scratched, as shown in FIG. 2A, can be processed to obtain a smooth surface from which a scratch 22 has disappeared.

When the spray etching process is performed for the exposed metal film 12 surface, as shown in FIG. 2B, only the exposed surface of the metal film 12 is selectively etched, while the inner faces of the scratch 22 are not.

Therefore, since spray etching is used, the foreign resin substance 20 and the scratch 22, as shown in FIG. 2C, have disappeared, and the exposed surface of the metal film 12 is smoothed.

As a result, a uniform protective metal layer 16 can be deposited, using either electroplating or electroless plating, on the exposed surface of the metal film 12 that has been smoothed.

EXAMPLE

To begin the explanation of an example, as illustrated in FIG. 3A, a plurality of pad faces 12 a are arranged on one face of a printed circuit board. As these pad faces 12 a, metal films 12 are formed, using electrolytic copper plating, that are exposed through a resin layer 14, which is thereafter formed using a solder resist.

On one of the pad faces 12 a, at a location encircled by a white dotted line, a foreign resin substance is attached, as shown in FIG. 3A.

The printed circuit board is then placed in a chamber under a reduced pressure of 300 Pa, and the plasma treatment process is performed by irradiating the pad faces 12 a for 300 seconds with a plasma that employed O₂ gas and had an output of 300 W.

Then, when following the plasma treatment process the resultant printed circuit board is observed using a microscope, it could be seen that the surface of the foreign resin substance had been roughened and had a sponge-like appearance. The surface of the resin layer 14, however, is only slightly roughened, and on the whole, the state of the resin layer 14 is almost the same as before the plasma treatment process is performed.

Then, during a spray etching process, an etching fluid, for etching the copper that forms the pad faces 12 a on the printed circuit board, is ejected through a nozzle, under a pressure of 0.2 MPa, and sprayed onto the pad faces 12 a, and the surface layers of the pad faces 12 a are etched to a depth of about 2 μm. For this spray etching process, a distance of about 100 mm is set between the distal end of the nozzle and the pad faces 12 a.

Following this, to evaluate the results obtained by the spray etching process, the pad faces 12 a are observed using a microscope, and it is found, as shown in FIG. 3B, that the foreign resin substance 20, previously located within the area encircled by the white dotted line on the one pad face 12 a, had been completely removed.

In order to provide more evenly smoothed pad face 12 a surfaces following the removal of the foreign resin substance 20, further etching of the pad faces 12 a may be performed using dip etching, for which a printed circuit board is immersed in an etching fluid.

In this example, a foreign resin substance, originally a solder resist, has been removed. However, so long as a material, a substance, can be roughened by performing a plasma treatment process, an arbitrary foreign resin substance formed by an organic material other than solder resist can be removed by performing spray etching, after the plasma treatment process has been performed in the same manner as in the example.

COMPARISON EXAMPLE

A printed circuit board is employed in this example, whereon pad faces 12 a, 12 a . . . made of copper shown in FIG. 4A, are exposed through a resin layer 14 formed of a solder resist, and a foreign resin substance is attached to one of the pad faces 12 a at a location encircled by a white dotted line as shown in FIG. 4A. The surface treatment process is performed in the same manner as in the example, except that instead of performing spray etching, the printed circuit board is immersed in an etching fluid, whereby the pad faces 12 a are etched to a depth of about 3 μm.

FIG. 4B is a diagram showing a microscope photograph of the pad faces 12 a on the printed circuit board obtained after the etching process had been performed. As shown in FIG. 4B, the foreign resin substance shown in FIG. 4A, which is attached to the pad face 12 a of the printed circuit board before the plasma treatment process, had not been removed from the location encircled by the white dotted line. 

1. A surface treatment method comprising the steps of: preparing a surface of a metal film exposed through a resin layer, including a foreign resin substance attached to the surface; performing a plasma treatment process for the surface so as to roughen the foreign resin substance without substantially damaging the resin layer; and etching the entire exposed surface of the metal film, with using a spray etching method for which an etching fluid is ejected through a nozzle to remove the foreign resin substance from the exposed surface.
 2. The surface treatment method according to claim 1, wherein the metal film is deposited on at least one face of a printed circuit board, and the surface of the metal film exposed through the resin layer is located on the same circuit board side as a pad on which an external connection terminal is formed.
 3. The surface treatment method according to claim 1, wherein a copper film is deposited, as a metal film, and soft etching is performed, with using a spray etching method, so as to remove an oxide film from an exposed surface of the copper film.
 4. The surface treatment method according to claim 1, wherein a metal plated film is deposited with using plating as the metal film.
 5. The surface treatment method according to claim 1, wherein the pressure setting for the ejection, through the nozzle, of the etching fluid is from 0.1 to 0.3 MPa.
 6. A surface treatment method comprising the steps of: preparing a surface of a metal film exposed through a resin layer, including a scratch formed on the surface, and etching the entire exposed surface of the metal film, with using a spray etching method for which an etching fluid is ejected through a nozzle to remove the scratch from the exposed surface.
 7. The surface treatment method according to claim 6, wherein the metal film is deposited on at least one face of a printed circuit board, and the surface of the metal film exposed through the resin layer is located on the same circuit board side as a pad on which an external connection terminal is formed.
 8. The surface treatment method according to claim 6, wherein a copper film is deposited, as a metal film, and soft etching is performed, with using a spray etching method, so as to remove an oxide film from an exposed surface of the copper film.
 9. The surface treatment method according to claim 6, wherein a metal plated film is deposited with using plating as the metal film.
 10. The surface treatment method according to claim 6, wherein the pressure setting for the ejection, through the nozzle, of the etching fluid is from 0.1 to 0.3 MPa. 